Flexible perovskite solar cells (f-PSCs) have recently reached power conversion efficiency (PCE) as high as 20.7% [1]. Although still lagging behind their rigid counterparts on glass, which in very short time have achieved 25.7% of certified efficiency [2],  the use of flexible substrates opens up to a wide range of applications, from sensors for the Internet of Things, to the retrofitting of existing buildings to improve their energy efficiency (building-applied PV), to space, thanks above all to the high power/to weight ratio generated wich is the range of 29.4 W/g compared to 8.31 W/g for amorphous silicon and 0.254 W/g for ultra-thin CdS / CdTe. [3] 

Here we present the synthesis of poly-3-hexylthiophene (P3HT)-derivated HTMs, embodying benzothiadiazole (BDT) moieties as electron-poor host, used as hole transport material (HTM) in f-PSCs. The use of this material led to PCE comparable to commercially available P3HT and showed improved stability under continuous illumination. It was also employed in 6×6 cm² modules, delivering 6.9% efficiency on 16 cm² of active area and demonstrating its feasibility for large area manufacture. [4]

Considering f-PSCs great potential for space application, the modified f-PSC were then tested under the effect of fast neutrons (i.e. with energies > 10 MeV) irradiation, which represent one of the most severe forms of radiation at aircraft altitudes, in avionic, and space environments. The stability of unencapsulated flexible perovskite solar cells against fast neutron irradiation was evaluated at two different fluence levels (1.39 × 10⁹ neutrons·cm^-2 - almost 80 years of fast neutron exposure on the International Space Station and 1.62 × 10¹⁰ neutrons·cm^-2 equivalent to 864 years of fast neutron exposure on the International Space Station), comparing commercially available spiro-OMeTAD, commercial P3HT and the in-house modified P3HT. We observed degradation for both materials and at both fluences. 

We observed that modified-P3HT cells experienced smaller voltage and current losses compared to spiro-OMeTAD but the overall performance suffered a much higher drop, as a consequence of a larger decrease in fill factor, ascribable to a sub-optimal perovskite/polymer interface. Nonetheless, spectral response and behavior at different light intensities of modified-P3HT cells suggest the polymer to be potentially more resilient than spiro-OMeTAD under fast neutron irradiation, once the perovskite/polymer will be improved [5].